<!DOCTYPE html>   
<html>   
<head>   
<meta charset=" utf-8">   
<meta name="author" content="http://www.softwhy.com/" /> 
<title>CSS如何实现弹出一个全屏灰黑色透明遮罩效果-蚂蚁部落</title>
<style type="text/css">
*
{
 margin:0px;
 padding:0px;
}
.zhezhao
{
 width:100%;
 height:100%;
 background-color:#000;
 filter:alpha(opacity=50);
 -moz-opacity:0.5;
 opacity:0.5;
 position:absolute;
 left:0px;
 top:0px;
 display:none;
 z-index:1000;
}
.login
{
 width:280px;
 height:180px;
 position:absolute;
 top:200px;
 left:50%;
 background-color:#000;
 margin-left:-140px;
 display:none;
 z-index:1500;
}
.content
{
 margin-top:50px;
 color:red;
 line-height:200px;
 height:200px;
 text-align:center;
}
</style>
<script type="text/javascript">
window.onload=function()
{
 var zhezhao=document.getElementById("zhezhao");
 var login=document.getElementById("login");
 var bt=document.getElementById("bt");
 var btclose=document.getElementById("btclose");
 
 bt.onclick=function()
 {
  zhezhao.style.display="block";
  login.style.display="block";
 }
 btclose.onclick=function()
 {
  zhezhao.style.display="none";
  login.style.display="none"; 
 }
}
</script>
</head>
<body>
  <div class="zhezhao" id="zhezhao"></div>
  <div class="login" id="login"><button id="btclose">点击关闭</button></div> 
  <div class="content">蚂蚁部落欢迎您，<button id="bt">点击弹出遮罩</button></div>
</body>
</html>